1. Field of the Invention
The present invention relates to a time information obtaining device and a radio-controlled timepiece.
2. Description of the Related Art
Conventionally, there is an electronic timepiece which receives a radio wave including time information, and automatically calibrates the time so as to be able to maintain display of the accurate time. As a radio wave which includes the time information, there is an airwave called a standard radio wave which transmits encoded time information with a radio wave in a long wavelength band. Various electronic timepieces (radio-controlled timepieces) which receive such standard radio wave to obtain time information are being developed.
The radio wave in the long wavelength band is transmitted long distances throughout the surface of the Earth. Therefore, it is possible to receive and use the standard radio wave at a point far from a transmission station. However, noise which is generated in the same wavelength band is also similarly transmitted long distances. Moreover, the radio wave attenuates inside a building made of a steel frame or reinforced concrete. Therefore, various techniques to enhance receiving sensitivity and to cope with noise are being developed in radio-controlled timepieces.
Specifically, in an electronic timepiece where the power capacity is small due to weight and size as in a watch, since the power consumed when the radio wave is received is very large, a technique is developed to promptly cancel or interrupt reception when the state of reception is bad and it is unlikely that the time information can be obtained. For example, Japanese Patent Application Laid-Open Publication No. 2012-189558 discloses a technique to judge the radio wave reception intensity based on AGC (automatic gain control) voltage or a technique to judge noise intensity based on degree of accuracy of deciding the position of change of the signal (amplitude) intensity.
However, if the noise is mixed at an important timing for determining the code when the standard radio wave is received, it becomes difficult to determine the code. When the noise mixed in the standard radio wave is a sudden noise (burst noise) instead of continuous noise, conventional methods cannot accurately judge the influence of the noise to judge whether to continue or cancel reception of the radio wave.
The present invention is a time information obtaining device and a radio-controlled timepiece which can more accurately judge whether or not to obtain time information and which can cancel the reception of the radio wave during the reception.